Field of the Invention
The invention relates to a process for producing a catalyst containing a catalytically active molybdenum-vanadium-oxygen phase (Mo--V--C phase) and/or a molybdenum-vanadium-titanium-oxygen phase (Mo--V--Ti--O), to a catalyst produced by the process and to a catalyst carrier body for the catalyst. The catalyst is particularly suitable for the catalytic conversion of nitrogen oxides (NO.sub.x) contained in exhaust gas or flue gas and is generally referred to as a DeNO.sub.x catalyst.
Published European Patent Application 0 470 334 A1, corresponding to U.S. Pat. No. 5,270,277, discloses an arsenic-resistant DeNO.sub.x catalyst and a process for producing it. In the application of the production process disclosed in that patent specification, an oxygen-rich Mo--V--O phase is produced which is cooled, ground and then subjected to a reducing treatment. In that treatment, oxygen defect sites are produced. The material so obtained is then ground, processed with additives to form a slip, applied to a support material such as, for example, expanded metal, and calcined together with the latter. The catalyst which is produced by that process as disclosed in the above-mentioned patent and application, is notable for an appreciable arsenic resistance and good catalytic activity in the reduction of nitrogen oxides with ammonia. However, in the case of that process the pure preparation of an oxygen-rich or low-oxygen Mo--V--O phase is virtually only possible with a disproportionately high expenditure. If that expenditure is not made, V.sub.2 O.sub.5 precipitates, for example, may catalyze undesirable side reactions. Thus, it is known, for example, that in addition to the desired catalytic activity in the reduction of nitrogen oxides with NH.sub.3, V.sub.2 O.sub.5 also develops an undesirable catalytic activity in the SO.sub.2 --SO.sub.3 conversion, which results in the formation of ammonium sulfate and/or ammonium hydrogen sulfate and in the case of a drop below the dewpoint of the sulfates, it leads to a gradual congestion of downstream components with the ammonium sulfate and/or the ammonium hydrogen sulfate.